The present invention relates to a method for manufacturing a blade, in which at least the composite base structure of the blade is manufactured in a pultrusion process by pulling fibres through at least an impregnation stage and a curing stage, the base structure is equipped with at least one wear area, and the said blade is detached from a blade blank formed of a base structure and a wear area.
In addition, the invention also concerns a blade manufactured according to the method, structural components of a blade, and their manufacturing methods.
Nowadays, composite blades are used in, for example, in doctors of paper machines. The base materials of the blades can be, such as, for example, a polymer material, such as a thermoset or a thermoplastic. One or more fibre reinforcements may have been added to the polymer structure, such as, for example, carbon, glass, and/or boron fibres and/or other continuous fibres, such as, for example, metal fibres. The orientation of such fibres can be used to give elongated blades excellent strength and stiffness. The fibres are bound to a polymer matrix, so that together they form a plate-like and rigid composite structure.
One advantage of composite blades is that they combine lightness with good strength and a gentle effect on the roll surface being doctored, without this detracting, however, from their doctoring power.
Finnish patent FI-101637 (PCT publication WO-99/12726 A1) discloses one form of the prior art relating to composite blades. It presents a doctor blade manufactured using a pultrusion method, in which grinding particles are combined with the fibre reinforcement. These are used to achieve a cleaning and servicing effect on the object being doctored. The servicing layer, in which the grinding particles are incorporated, can be formed by bringing it into contact with carbon fibres, for example, by impregnating a carbon-fibre fabric with a matrix agent. The grinding particles can be along at least one edge of the blade, which then forms the wear area, the ‘work edge’ of the blade.
Another form of the prior art is disclosed in Finnish patent application FI-981312 (PCT publication WO-99/64674 A1). In it, the blade is also manufactured from a composite material, for example in a pultrusion process, while the surface of the wear area is given a ceramic coating. The ceramic is attached by an anchor structure to the surface of the composite. The anchor structure is attached throughout to the composite. A ceramic coating is manufactured to the surface of the composite, for example, with the aid of thermal spraying or some other suitable process. The process of making the coating takes place essentially separately from the actual pultrusion process. This complicates the production of blades.
A third example of composite blades is disclosed in U.S. Pat. No. 4,549,933.
At present, blades structures like those described are pulled through the pultrusion process, for example, with the aid of glass-fibre reinforcements which are cast into the base structure of the blade in the pultrusion process. Arranging reinforcements purely for the purpose of pulling increases the manufacturing costs of a blade. In addition, the working tolerance of the blade remains quite limited, as the grinding particles are bound to the base structure of the blade i.e., to the carbon-fibre composite, which wears easily, or because the thickness of the ceramic coating anchored to the composite is otherwise limited.